The present invention is directed to a bellows or boot for hydraulic, hydropneumatic or pneumatic piston-cylinder units, and particularly for vibration dampers or spring struts for vehicles, wherein the boot covers the portion of the piston rod that projects from the cylinder to protect against dirt and/or damage and is arranged between the end of the piston rod and the cylinder, the interior space of the boot undergoes a change in volume due to the relative movement of the parts with respect to one another, and at least one flow connection is provided which leads to the interior space of the boot and allows air to flow in and/or out.
Boots for piston-cylinder units in which a vibration damper or a spring strut is provided with a boot for protecting against dirt and/or damage are already known from German patent document DE 102 00 608 A1. Due to the relative movement between the piston rod and the cylinder, the interior space of the boot undergoes a change in volume, for which purpose an opening leading to the interior space of the boot is provided so that air can flow in and out. The air inlet and air outlet generate an air flow by which water or dirt particles that have penetrated via an outlet valve are conveyed back into the atmosphere.
Austrian patent document OE 324 144 further discloses a boot with openings for venting the interior space, the openings on the piston rod side are covered by a packing to protect against water and dirt particles. The packing is a component part of the boot and, if necessary, a ring-shaped filter adapted to the space can be introduced between the openings and the packing. This construction has the disadvantage that water and dirt particles, even in small amounts, can enter the interior of the boot and remain there owing to the lack of an outlet opening. As a result, the piston rod and the guide component are highly susceptible to corrosion, which can ultimately lead to failure of the piston-cylinder unit.